Committed to master branch by mistake? Do not solve it by branching off a feature branch and then reverting that commit on master. You will lose changes in that commit - they will not be merged back from the feature branch.

Suppose we have done a commit (2) by mistake to master (it should have been on a feature branch to be merged to master later):

We can smartly solve it by branching off feature branch now and then create a commit reverting commit 2 on master:

git branch feature
git revert HEAD

This is how it looks like now:

In fact, this is what we want. The branch feature contains the changes in commit 2. The branch master does not contain them, because they were reverted by commit 2’.

Now, let’s work on that branches. Create some commit on master (3) and some other unrelated commit on feature (4):

Later it’s time to merge feature back to master, because we finished the work on feature:

git checkout master
git merge feature

The result will look like this:

This looks fine. However, we do not have the changes made in commit 2. Git knows that 2 is an ancestor of master and thus is already included in master. Of course, the change is not included, because we reverted it afterwards. So, we have lost the change. If many other changes have been done on feature, we can easily overlook this.

In fact, this happens even if doing rebase instead of merge:

git checkout feature
git rebase master

Here is a whole script that shows this situation (note that at the end, the file f does not contain the line “some change” - added in that reverted commit):

#!/bin/bash

set -e
set -u

mkdir test
cd test
git init

# A

touch f
git add f
echo "initial" >> f
git commit -am "1_initial"

echo "some change" >> f
git commit -am "2_some change"

# B

git branch feature
git revert HEAD

# C

echo "other change on master" >> f_master
git add f_master
git commit -am "3_other change on master"

git checkout feature

echo "other change on feature" >> f_feature
git add f_feature
git commit -am "4_other change on feature"

# D

git checkout master
git merge feature
#git checkout feature
#git rebase master